Various dyes have been used previously to develop contrasts between portions of a fibrous specimen studied with microscopic evaluation techniques. Information about the fiber sample may be determined by comparing the dyeing characteristics of the fibers to known characteristics. For instance, the presence and distribution of starch in the fiber may be determined by examining microscopically a dyed fibrous material. Prior to evaluation, the fibrous material is usually stained by immersion in a one percent aqueous or alcoholic solution of the dye. Such immersion is generally at room temperature or warmed for a period of time. The excess dye solution is washed and the fabric dried prior to evaluation.
An article entitled "Microscopical Techniques in Finishing Research" presented at the American Association of Textile Chemists and Colorists identified various solutions for staining fabrics prior to microscopic examination. For instance, iodine which colors starch purple or black may be used to detect the presence and uniformity of distribution of starch. The presence and location of polymeric impregnant can be shown because melamine resins can be dyed with several wool dyes, such as CI Acid Blue 1. Waxes may be colored with solvent dyes, and brief boiling of the fiber sample in 95 percent ethanol prior to staining enhances the depth of shade. Pectin and associated compounds yielding glucoronic residues on hydrolysis are stained by basic dyes. Proteins may be stained with acid or basic dyes depending on pH conditions.
Russian Pat. No. 127,462 describes examining paper fiber orientation by reflective light with a magnifying glass, microscope or other optical apparatus. The structure is shown more clearly if the sample is moistened with a three to five percent solution of hydrochloric acid and dried at 105.degree. C. for five to ten minutes until the sample darkens.
Russian Pat. No. 444,072 describes a binder distribution determination method for nonwoven fabrics. A latex such as carboxylbutadiene-acrylonitrile SKN-40-1 GP is mixed with a 6.95 to 7.05 g/l dichlorotriazine reactive dye and then reacted at room temperature for about ten hours in the presence of sodium bicarbonate (NaHCO.sub.3) before applying to the fabric. Such a compound may be used to impregnate black fabrics for analysis.
Russian Pat. No. 521,514 describes a method of determining the content of cotton seed shell in cotton fiber with ammonium molybdate which colors the tannin in the seed shell tissues. Where there is an intensive accumulation of tannin, which is a measure of the strength of the seed shell, the fiber sample assumes a dark orange color. Where the seed shell is less strong, i.e., the accumulation of tannin is small, the sample assumes a yellow color.
U.S. Pat. No. 3,190,724 describes testing cotton to determine damage by microorganisms. The test method moistens the fabric sample with a pH indicator solution substantially free of oxygen by using an inert propellent gas. The color of the indicator solution on the cotton sample is compared with the color of the indicator solution at various pH levels to determine the extent of damage, if any, to the cotton.
U.S. Pat. No. 3,576,713 describes a process of determining the ionic character of starches, wood pulps, paper masses, and paper surfaces by mixing them with solutions of organic coloring materials which show changes in the range of visible light in accordance with the ionic character of the materials. The reference describes using potassium salts of tetrabromo and tetraiododichlorofluorescein and coloring materials of triphenylmethane series, preferably chlorides of triamino and chlorides and oxalates of tetramethyltriphenylmethane.
Reliable microscopy requires that the cellulose fibers be stained. The Institute of Paper Chemistry discusses in Paper and Fiber Analysis various triiodide stains for microscopy work. Some triiodide stains use potassium triiodide and multicomponent salt solutions in a one-step application stain; another triiodide stain uses potassium triiodide and sulfuric acid in a two-step application. These multicomponent salt solution stains cannot tolerate even slight dilution with water and are limited to use on dried cellulose fiber samples. Such stains also are generally sensitive to light, have a relatively short shelf life and take some time to prepare. Further, preparation and use of the potassium triiodide sulfuric acid stain is potentially hazardous.
Known triiodide stains generally involve the use of concentrated aqueous salt solutions. For example, some of the more widely used triidido stains are Graff "C" stain, the Herzberg stain, the Sutermeister, the Jenke stain, and the Selleger stain. The Graff "C" stain is made by the addition of potassium triiodide solution to a concentrated mixture of aluminum chloride, calcium chloride and zinc chloride solutions. The Herzberg stain combines potassium triiodide solution with a concentrated zinc chloride solution. The Sutermeister stain is made by adding potassium triiodide solution to a saturated calcium chloride solution. The Jenke stain combines solutions of potassium triiodide and saturated magnesium chloride. The Selleger stain is a mixture of potassium triiodide solution and a concentrated calcium nitrate solution. As mentioned above, these stains are impractical to use on wet fibers because any dilution of the stain with water renders the stain inoperative. These stains have other drawbacks which limit their usefulness. One problem is that the triiodide stains are unstable. For example, the stains are light sensitive and easily oxidized. The stains must therefore be stored in a refrigerator in small quantities in stoppered dark glass bottles to minimize the air oxidation and the light degradation of the stain.
Thus, there exists a need in the art for a stain solution for fiber evaluation that is free of the problems typically found when preparing and using fiber evaluation stains.